1. Field of the Invention
The present invention is directed to a hearing aid of the type having a directional microphone system, an earphone and a number of microphones. The invention is also directed to a method for the operation of a hearing aid having a directional microphone system, the hearing aid containing a signal processing unit, an earphone and a number of microphones.
2. Description of the Prior Art
Hearing aids having a directional microphone system composed of a non-directional microphone and a directional microphone directed toward the front are known, and allow the user to switch between the individual microphones by pressing a button (European Application 0 499 699). When the directional microphone directed toward the front is activated, speech comprehension improves given unwanted sound coming mainly from the side and from the back and given useful sound (i.e., audio signals which the user desires to hear) directly incident from the front. Given activation of the non-directional microphone, a good and natural speech comprehension is achieved given useful signals incident from all sides.
U.S. Pat. No. 4,751,738 discloses a hearing aid with a directional microphone system having a signal processing unit, an earphone and a number of microphones. Spaced microphones are employed whose output signals can be interconnected with one another with different weightings on the basis of different filter curves, for producing an individual directional microphone characteristic, particularly by processing in the signal processing unit (amplifier stage, summing stage and filter stage).
In some auditory situations, for example given useful sound incident from the side and from behind, such hearing aids having a non-directional microphone and a directional microphone directed toward the front allow only limited speech comprehension.
An object of the present invention is to provide a hearing aid as well as a method for the operation of a hearing aid of the type initially described wherein improved speech comprehension is achieved for an optimally large number of auditory situations, including even auditory situations that rarely occur.
The above object is achieved in an inventive hearing aid having a number of microphonesxe2x80x94non-directional or directional microphones, the respective output signals of which being interconnectable with one another with different weightings and with different delays, resulting in a directional microphone characteristic adapted to the individual auditory situation. By appropriate weighting and delay of the microphone output signals, useful signals incident, for example, from the side and from behind can thereby be appropriately acquired, for example during a mountain hike next to a babbling brook.
The interconnection of the microphones can ensue in pairs (directional characteristic of the first order) or can incorporate three or more microphones (directional characteristic of a higher order).
Overall, the directional microphone system of the inventive hearing aid is composed of a number of individual microphones having different principal directions. Either individual directional microphones or a combination of two non-directional microphones can be employed as microphones in conjunction with an electronic signal processing circuit for weighting and different delay of the respective output signals of the non-directional microphones.
Due to a multiple utilization of non-directional microphones, the number of sound admission openings required in the hearing aid housing can be reduced, so that, for example, the front, back, left, right, top and bottom directions can be xe2x80x9ccoveredxe2x80x9d with four non-directional microphones and respective additional electronic circuits for weighting and delay of the output signals of the non-directional microphones.
When the hearing aid is fashioned as a behind-the-ear (BTE) hearing aid, the individual microphones forming the directional microphone system can be attached to the main body of the hearing aid with an appropriate alignment of the sound admission openings. For example, four microphones can be provided for picking up sound from the front, back, below and from the side.
By attaching auxiliary members to the main member of the BTE hearing aid, microphones having corresponding sound admission openings that also allow further sound incident directions, for example lateral directions, to be taken into consideration, can be attached in the auxiliary member.
Such an auxiliary member attached to the main member can be fashioned as a hinged, lever-like element. Dependent on the respective auditory situation, the user can swing the auxiliary member out on the hinge to an xe2x80x9cactivexe2x80x9d position and thereby align the microphones contained in the auxiliary member, and given a change in the auditory situation, can again swing the auxiliary member back against the main member to a space-saving, xe2x80x9cretractedxe2x80x9d position.
The auxiliary member can be fashioned as a tear-shaped or arcuate lever-like element, so that it has an optical approximation of an earing. As a result, the overall optical impression of the BTE hearing aid is improved.
When the hearing aid is fashioned as an in-the-ear (ITE) hearing aid, at least three microphones can be integrated into the main member of the ITE hearing aid. Advantageous directional properties are achieved when the sound admission openings of the three microphones are arranged on connecting lines crossing one another substantially at a right angle.
An auxiliary member that is implemented as a hinged, lever-like element can also be attached to the main member of an ITE hearing aid. Further microphones can be integrated in this auxiliary member, allowing further, for example lateral, sound incidence directions to be acquired supplementing the microphones contained in the main member.
The inventive method of the operation of a hearing aid having a directional microphone system includes the step of selectively setting the principal direction of the directional microphone system in adaptation to the existing auditory situation. By employing a number of microphones, a multitude of different principal directions can be set, allowing useful sound incident from the side or from the back to be taken into consideration.
In a normal position, the principal direction xe2x80x9cfrontxe2x80x9d is preferably set in the directional microphone system, so that useful signals incident from the front, for example when two persons standing opposite one another are talking, can be acquired.
The inventive method allows the principal direction to be set over a wide range of variation, so that a complete auditory situation occurring, for example, on a mountain hike can be received and heard with the useful signals incident from the side and from behind.
In the inventive method, it is preferably first determined from which direction the strongest useful signals are incident in order to align the principal direction of the directional microphone system in accord therewith. The maximum of the sound energy or of the acoustic pressure can be employed as a criterion for determining the principal direction.
Switching from a previously set principal signal direction can ensue dependent on various criteria. The respective criteria can be stored as thresholds in the hearing aid, so that a change of the principal signal direction ensues when one or more such thresholds is/are exceeded. The principal direction of the directional microphone system can be set as a switching criterion dependent on the modulation frequency of the output signals of the individual microphones (dependent on brief-duration fluctuations of the frequencies of the reception signals).
The modulation boost (level difference between briefly loud and soft reception signals) or the absolute frequency spectrum of the output signals of the individual microphones can be employed as further switching criteria.
The difference of the frequency spectra of the signals picked up from various directions can be employed as a further switching criterion. When this difference deviates from a stored reference value, switching of the principal direction of the directional microphone system can ensue.
Further switching criteria are the absolute levels of the output signals of the individual microphones as well as the level difference of a brief-duration peak level value from the average of the level of the output signals of the microphones.
When switching the principal direction, the frequency of the upward transgression of defined level differences of signals from different directions of the output signals of the individual microphones also can be taken into consideration. As a result, an excessively frequent switching of the principal signal direction of the directional microphone system, which could result in a disquieting sound impression for the user, can be avoided.
The individual switching criteria can be continuously acquired and effect a continuous, current adaptation of the principle signal direction. Alternatively, an automatic restoration of (default to) the principal direction of xe2x80x9cfrontxe2x80x9d can ensue if no new switching direction pulses are registered after a defined time.
In order to avoid a signal distortion in the combining of the output signals, for example of the non-directional microphones, the output signals thereof are boosted before being combined with the output signals of other microphones, particularly in the range of low frequencies. In general, frequency response fading which may occur in the output signals of the respective microphones can be compensated by an equalizer.
If the hearing loss is different in the two ears of the hearing aid user, the frequency responses of the individual microphones are individually adapted to the respective hearing losses for the different directions, so that the user can already identify the main sound incidence direction with one ear.
In a further version of the method, different main signal directions are set in two microphone systems in a biaural system for the left ear and the right ear of the user, respectively, in order, for example, to be hear toward the front with one hearing aid and toward the side and toward the back with the other hearing aid. For example, this can be advantageous when traveling by automobile.
A single-channel or multi-channel AGC (automatic gain control) in the hearing aid can be differently adapted for the different level ranges in the respective response and decay times.
In further versions of the method, further, an angle between a straight line through two microphones of the hearing aid and the horizontal or vertical caused by the shape of the user""s ear can be compensated. It is thus simulated that the respective microphones involved in the compensation seem to be located directly in the horizontal direction or vertical direction, despite their actual skewed position.
In order to implement a switching of the principle signal direction of the directional microphone system in an especially pleasant way and in order to avoid abrupt switching noises, the use of fuzzy electronics can be advantageous.